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The Effects of Dietary Histidine, Methionine and Homocystine on Vitamin B,, and Folate Levels in Rat Liver

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The Effects of Dietary Histidine, Methionine and Homocystine on Vitamin B,, and Folate Levels in Rat Liver Downloaded from 299 https://www.cambridge.org/core The effects of dietary histidine, methionine and homocystine on vitamin B,, and folate levels in rat liver BY D. L. WILLIAMS AND G. H. SPRAY Nuftield Department of Clinical Medicine, Rndclaze InJirmary, Oxford OX2 6HE . IP address: (Received 12 May 1975 -Accepted 4 Novembw 1975) 170.106.202.8 I. L-histidine (20 g/kg) added to vitamin Bl,-deficient and cyanocobalamin-supplemented diets based on soya-bean flour reduced the growth of rats given the vitamin B,,-deficient diet but stimulated growth of rats given the cyanocobalamin-supplemented diet. Liver weight (g/kg body-weight) increased, but the protein content of the livers decreased, in rats given , on histidine supplements. The histidine was associated with significantly higher folate con- 28 Sep 2021 at 17:30:18 centrations in the livers of cyanocobalamin-supplemented rats. 2. Vitamin B1,-deficient and cyanocobalamin-supplementedrats were given diets based on a mixture of amino acids that was balanced apart from methionine, which was added in various amounts, and with the addition of homocystine. The only vitamin B,,-deficient rats which had reasonable gains in weight were those receiving a diet containing 8 g L-methionine/kg. The remainder, particularly those given diets containing only homocystine, had little or no increase in weight. All the cyanocobalamin-supplemented rats gained weight; those given diets containing 2 and 8 g L-methionine/kg, or 8 g homocystine/kg, had the highest gains. , subject to the Cambridge Core terms of use, available at 3. There was a tendency for a higher concentration of either methionine or homocystine in the diet to be associated with higher concentrations of both folate and vitamin Biz in the livers. 4. In vitamin Bla deficiency methionine appeared to increase the accumulation of folate in the liver, affecting mainly the amounts of polyglutamate derivatives. This work was begun to study the influence of vitamin B,, deficiency on some of the enzymes involved in folate metabolism. For various reasons the results for the enzymes cannot be reported. However, the study produced some interesting results on the effects of different diets on folate and vitamin B,, levels in liver, on liver weight and protein content, and on the growth of the animals. These results are reported in this paper. The first part of the study involved the addition of supplementary histidine to the vitamin B,,-deficient and cyanocobalamin-supplemented diets described previously https://www.cambridge.org/core/terms (Williams, Spray, Newman & O’Brien, 1969). It seemed possible that extra tetra- hydrofolic acid might be required to react with the formiminoglutamic acid formed during the metabolic breakdown of histidine; folate balance might therefore be affected. Methionine influences folate metabolism in vitamin B,, deficiency (Silverman & Pitney, 1958; Kutzbach, Galloway & Stokstad, 1967; Smith, Osborne-White & Gawthorne, 1974). It was therefore of interest to study the effects of vitamin B,, deficiency on folate metabolism in rats maintained on synthetic diets containing a . mixture of amino acids instead of protein. With these diets, individual amino acids https://doi.org/10.1079/BJN19760038 can be eliminated, and their relative proportions varied with certainty; this is virtually impossible with diets containing proteins. Kutzbach et al. (1967) used a mixture of this type to provide a ‘labile-methyl’-free diet. Downloaded from D. L. WILLIAMS AND G. H. SPRAY I976 https://www.cambridge.org/core EXPERIMENTAL Amino acid diets. These were based on agar-gel diets (Rogers & Harper, 1965)and contained (/kg): IOO g maize oil, 50 g salt mixture, 2 g choline dihydrogen citrate, 185 g L-amino acid mixture, 436 g starch, 216g sucrose, 10g water-soluble vitamin mixture, I ml fat-soluble vitamin mixture. The salt mixture was the same as that used by Rogers & Harper (1965; p. 268, footnote 3). The amino acid mixture was that recommended for diet no. I of Rogers & Harper (1965; Table 2), including . IP address: asparagine, arginine HCI, and all amino acids listed in footnote z of the Table except methionine. The vitamin mixtures had the same composition as those used in the soya-bean-flour (soya) diets described by Williams et al. (1969)except that the 170.106.202.8 amount of cyanocobalamin (when included) was increased to 75 pg/kg diet. When L-methionine or DL-homocystine were added, the corresponding amounts of starch were omitted. , on 28 Sep 2021 at 17:30:18 Animals and their management. Male and female weanling albino rats of the Wistar strain (Scientific Products Farm Division, Charles River UK Ltd, Manston Road, Margate, Kent) were fed on a stock diet (modified diet 41b; Herbert C. Styles (Bewdley) Ltd, Severn Side Mills, Bewdley, Worcestershire ; supplied by Oxoid Ltd, Southwark Bridge Road, London SE I) until they were mated. After mating, the females were given the soya diets (Williams et aE. 1969) containing either no added , subject to the Cambridge Core terms of use, available at cyanocobalamin or 75 pg cyanocobalamin/kg diet ; they received the same diets throughout pregnancy and lactation. The male offspring were weaned onto and reared on the same diets as their dams until they weighed 100-1 50 g. They were then randomly assigned to dietary groups within each experimental group. The rats were housed in groups of ten (Expt I), eight (Expt z), eight or ten (Expt 3), or six, seven or eight (Expt 4), in plastic cages with tops and bases constructed of stainless-steel wire. The risk of coprophagy was minimal because the spaces between the bars of the floors were wide enough for faecal pellets to fall through. Food and water were supplied ad lib. No attempts were made to measure food intake because there was considerable spillage of food. The animals were weighed weekly. After the appropriate periods on the experimental diets they were killed. Expt I. Four groups, each of ten male rats weighing about IOO g, were fed on the https://www.cambridge.org/core/terms vitamin B1,-deficient soya diets with or without 20 g supplementary L-histidine/kg, or the corresponding cyanocobalamin-supplemented diets with and without histidine. After 7 weeks the survivors were killed by bleeding from the aorta under diethyl ether anaesthesia. The livers were removed, weighed and stored at - 19' until required for the assays. Expt 2. Two groups, each consisting of eight male rats (body-weight approximately 150g), were fed on the vitamin B,,-deficient amino acid diet with 8 g DL-homocystine added for 3 or 6 weeks, after which they were killed as described for Expt I.Two . further groups were given the cyanocobalamin-supplemented amino acid diet with https://doi.org/10.1079/BJN19760038 the same level of homocystine for the same periods, and two received vitamin BIZ- deficient or cyanocobalamin-supplemented amino acid diets containing 8 g L-methionine/kg. The latter groups were killed after 6 weeks. A seventh group Downloaded from Vol. 35 Amino acid nutrition and vitamins in liver 301 continued to receive the vitamin BIZ-deficient soya diet, and was killed after https://www.cambridge.org/core 3 weeks. Expt 3. Six groups of male rats that had been reared on the vitamin B1,-deficient soya diet and six groups reared on the cyanocobalamin-supplemented soya diet were given vitamin B,,-deficient or -supplemented amino acid diets containing various proportions of methionine or homocystine, or both (Table 3). Another group con- tinued to receive the cyanocobalamin-supplemented soya diet. Each group contained eight or ten rats, each weighing about IOO g at the start of the experiment. All the rats . IP address: that were given amino acid diets were killed after 4 weeks on the diets as described for Expt I ; those that continued on the soya diet were killed at the same time. Expt 4. Seven male rats were given the vitamin B,,-deficient amino acid diet con- 170.106.202.8 taining z g L-methionine/kg, and eight received a similar diet with 8 g L-methionine/ kg. Two other groups, of six and seven rats respectively, were given cyanocobalamin- supplemented diets with the same supplements of methionine. Each animal weighed , on 28 Sep 2021 at 17:30:18 about 150g when the experiment began; all were killed after they had been given the amino acid diets for 10weeks. In this experiment the rats were killed by cervical dislocation. The livers were rapidly removed and freeze-clamped between aluminium discs that had been cooled in liquid nitrogen (Wollenberger, Ristau & Schoffa, 1960). Determination of total folate content. Weighed portions of each liver were processed , subject to the Cambridge Core terms of use, available at by the method of Bennett, Berry, Chanarin & Ardeman (1964).In Expt 4 the frozen livers were ground to powder in mortars that had been cooled in liquid N,. Samples of the powders were treated as described by Osborne-White & Smith (I973), to avoid autolysis and possible breakdown of conjugated folates, to enable pteroylmono-, di- and triglutamate derivatives to be determined. Folate was determined by micro- biological assay with Lactobacillus casei as the test organism, as described by Spray (1964). Other methods. Vitamin B,, in liver was determined by the method of Booth & Spray (1960).Liver protein was estimated in diluted liver homogenates by the method of Lowry, Rosebrough, Farr & Randall (1951).All probabilities were cal- culated using Student’s t test. https://www.cambridge.org/core/terms RESULTS AND DISCUSSION Expt I. Addition of L-histidine (20 g/kg diet) to the vitamin B,,-deficient soya diet reduced the growth of rats significantly (Table I). Although rats fed on cyano- cobalamin-supplemented diets with supplementary histidine had a mean weight gain of 93 g in 7 weeks compared with only 66 g for rats not receiving histidine, the differ- ence was not quite significant (P > 0.05).
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